Parameter "k" is the number of standard deviations "σ" on either side of the mean "μ" for which a lower bound of the included distribution {fraction between (μ-kσ) and (μ+kσ)} is required {and given by this inequality to be (1 - 1/k2)}. See also Msg #4 at the following site (Form #1 in this Msg is most commonly used):